Light powered array

ABSTRACT

A sensor array includes a plurality of sensor locations at which sensed signals are produced. A tension element holds locations at a given maximum spacing. The tension element includes an optical fiber. Light propagating on the optical fiber is applied to converters at each location for generating electrical power for the electrically powered portions of the array. The electrically powered portions may be a part of the sensor suite at each location, telemetry equipment, or both.

FIELD OF THE INVENTION

[0001] This invention relates to sensor arrays, and more particularly tothe powering of sensors and sensor ancillary equipment from an opticalfiber.

BACKGROUND OF THE INVENTION

[0002] Sonar towed arrays may include a large number of acousticpressure sensors, as for example in the range of 200 to 700, spacedalong a tow line. In addition, non-acoustic sensors, such as hydrostaticpressure (depth), temperature, magnetic heading, pitch, and roll sensorsmay be placed at various locations along the tow line, including atthose locations associated with an acoustic pressure sensor. Inaddition, each sensor location is associated with a telemetryarrangement for transmitting the sensor signal, or at least a signalrelated to the sensor signal, to the towed end of the array. Thetelemetry equipment at each sensor location on the array must bepowered, so in addition to whatever electrically conductive or opticalsignal path or paths extend from the various sensors to the towed end ofthe array, there must also be electrically conductive power conductorsfor transmitting energization voltage to at least the telemetryequipment.

[0003] Improved sensor arrays are desired.

SUMMARY OF THE INVENTION

[0004] An array according to an aspect of the invention includes atleast a first sensor for sensing an environmental condition and forgenerating a first signal in response thereto, and a second sensor forsensing the environmental condition and for generating a second signalin response thereto. A tension element is coupled to the first andsecond sensors for tending to keep the first and second sensors at firstand second locations separated by a physical spacing no greater than agiven amount. A first electrically operated transducer is co-locatedwith the first sensor and electrically coupled thereto for receiving thefirst signal and for transmitting at least a signal related to the firstsignal to a node of the array. A second electrically operated transduceris co-located with the second sensor and electrically coupled theretofor receiving the second signal and for transmitting at least a signalrelated to the second signal to a node of the array. The first andsecond electrically operated transducers each include a terminal forreceiving energizing potential. A light-carrying optical fiber extendsbetween the first and second locations. A light-to-electric converterlocated at each of the first and second locations receives light fromthe optical fiber, and converts the light into the energizing potential.

[0005] In a particular embodiment, at least some of the sensors comprisepressure sensors, and may comprise acoustic pressure sensors. In anotherversion of this aspect, the tension element may comprise the opticalfiber. In one version of this aspect of the invention, thelight-to-electric converter may comprise a solar cell, and in anotherversion the light-to-electric converter comprises a photodiode.

[0006] In another version of this aspect of the invention, the firstsensor may comprise an acceleration sensor, and an integrator is coupledto the acceleration sensor for converting acceleration signals intovelocity signals. In a particular version of this aspect, the integratoris an electrically operated integrator including a terminal forreceiving the energizing potential. The acceleration sensor may includea micro electro mechanical system.

BRIEF DESCRIPTION OF THE DRAWING

[0007]FIG. 1 is a simplified diagram in block and schematic formillustrating a towed underwater array including plural sensor nodes;

[0008]FIG. 2 is a simplified diagram in block and schematic formillustrating some details of sensor nodes of the arrangement of FIG. 1;

[0009]FIG. 3 is a simplified diagram in block and schematic formillustrating some details of a typical light-to-electric converter whichmay be used at a location of FIG. 2;

[0010]FIG. 4 is a simplified diagram in block and schematic formillustrating some details of one possible embodiment of a sensor suiteof FIG. 2;

[0011]FIG. 5 is a simplified diagram in block and schematic formillustrating a first preferred embodiment according to an aspect of theinvention, in which fiber acoustic sensors and non-acoustic MEMS sensorsare used; and

[0012]FIG. 6 is a second preferred embodiment similar to FIG. 5, inwhich fiber acoustic sensors, MEMS acoustic and non-acoustic sensors areused.

[0013]FIG. 7 is another embodiment similar to FIG. 5 including a mix ofacoustic and non-acoustic fiber optic, MEMs, and conventional non-MEMssensors.

DESCRIPTION OF THE INVENTION

[0014]FIG. 1 is divided by a dash line 10 into “wet” and “dry” portions,corresponding to the ocean 1 and a boat or ship 2 thereon, respectively.A towed array designated generally as 12 includes a plurality of sensorlocations, two of which are designated 14 ₁ and 14 ₂, respectively.There may be additional sensor locations (not illustrated) remote fromthe dry portion of FIG. 1. Ship 2 may be considered to be a main or headnode of the array 12. A tension element designated as 16 extends fromthe ship to locations 14 ₁ and 14 ₂, for keeping the locations along thetension element at a substantially fixed separation, illustrated as S.Other locations (not illustrated) may be spaced apart by S or by someother distance, as the situation may require. The movement of the shipcauses the various portions of tension element 16 and the locationstherealong to trail behind the ship. The most remote portion of thetowed array 12 is illustrated as a remote end 16 re.

[0015] Tension element 16 of FIG. 1 includes an optical fiberillustrated as a line 16 f and also includes a telemetry conductorillustrated as a line 16 c. Line 16 c may also be part of amulticonductor cable, or may alternatively be a part of a coaxial cable.Preferably, telemetry line 16 c comprises an optical fiber fortransmitting optical signals representing the telemetry data flowingfrom each of the sensor locations to the dry signal processingelectronics. The telemetry data may include acoustic andor nonacousticsensor data. If necessary, it may also include a strength member, if thestrength of the optical fiber 16 f andor the electrical conductor 16 cis insufficient.

[0016] The dry side 2 of line 10 of FIG. 1 includes a source of lightillustrated as a block 20 coupled to the near end 16 ne of the opticalfiber 16 f, for propagating light through the fiber 16 f toward theremote end 16 re of the tension element 16. The dry side 2 of conductor16 c is coupled to a demultiplexer 22, if necessary to separate signalsreturning to the ship from the towed array 12. The demultiplexed signalsare applied to signal processing illustrated as block 24 for producingsignals representing organized sensed information, and the organizedinformation is made available for storage andor display, illustrated asblock 26.

[0017]FIG. 2 is a simplified diagram in block and schematic form,illustrating the constituents of any one of the locations 14 ₁, 14 ₂, .. . along the towed array. In FIG. 2, the locations are designated as 14₁ and 14 ₂ for definiteness. Location 14 ₁ includes a sensor suiteillustrated as a block 210 ₁. Sensor suite 210 ₁ may include acousticpressure sensors such as fiber optic acoustic sensors or micro electricmechanical systems (MEMS) acoustic sensors, and non-acoustic sensors fortemperature, hydrostatic pressure, heading or bearing, GPS, and thelike, including non-acoustic MEMS sensors, some or all of which mayrequire electrical energization or power. For the purpose of receivingelectrical energization power, block 210 ₁ is illustrated as includingan electrical terminal or electrode 210 e 1. The results of the sensingare produced as sensed signals at an output port 210 ₁o of block 210 ₁.The sensed signals are provided by a path illustrated as 211 ₁ totelemetry electronics, illustrated as a transducer block 212 ₁; thesignals flowing over path 211 ₁ are referred to as signals 211 ₁.Telemetry electronics 212 ₁ receives the various sensed signals, andprocesses them for transmission, as for example by digitizing,compression, andor preprocessing. The processed or transduced signalsproduced by telemetry electronics 212 ₁ are transmitted by way of anoutput port 212 o 1, a path 213 ₁, and a directional coupler 214 ₁ in anupstream direction over conductor 16, which is to say toward the dryportion 2 of the towing ship of FIG. 1, corresponding to the head ormain node of the array 12 of FIG. 1. The signals from telemetry block212 ₁ flowing over path 213 ₁ are referred to as a telemetry signal,which is related to the sensor signal. For purposes of being powered byelectrical energization, block 212 ₁ is illustrated as including anelectrical terminal or electrode 212 e 1. Location 14 ₂ includes asensor suite illustrated as a block 210 ₂. Sensor suite 210 ₂ mayinclude acoustic pressure sensors (including fiber optic acousticsensors), micro electric mechanical systems (MEMS) sensors, non-acousticsensors for temperature, hydrostatic pressure, heading or bearing, GPS,and the like (including non-acoustic MEMS sensors), some or all of whichmay require electrical energization or power. For the purpose ofreceiving electrical energization power, block 210 ₂ is illustrated asincluding an electrical terminal or electrode 210 e 2. The results ofthe sensing are produced as sensed signals at an output port 210 ₂o ofblock 210 ₂. The sensed signals are provided by a path illustrated as211 ₂ to telemetry electronics, illustrated as a block 212 ₂; thesignals flowing over path 211 ₂ are referred to as signals 211 ₂.Telemetry electronics 212 ₂ receives the various sensed signals, andprocesses them for transmission, as for example by digitizing,compression, andor preprocessing, and transmits the resulting processedsignal by way of an output port 212 o 2, a path 213 ₂, and a directionalcoupler 214 ₂ in an upstream direction, which is to say toward thetowing ship over conductor 16 c. The signals from telemetry block 212 ₂flowing over path 213 ₂ are referred to as a telemetry signal, which isrelated to the sensor signal. For purposes of being powered byelectrical energization, block 212 ₂ is illustrated as including anelectrical terminal or electrode 212 e 2.

[0018] According to an aspect of the invention, light is propagatedthrough optical fiber 16 f in a downstream direction from the ship 2,which is to say that the light propagates from main or head node 2toward remote end 16 re of the tension element, passing through all thelocations (only locations 14 ₁ and 14 ₂ illustrated). At location 14 ₁of FIG. 2, a portion of the light propagating through optical fiber 16 fis coupled by way of an optical sampler 214 ₁ to a light-to-electricconverter illustrated as a block 216 ₁. The optical sampler 214 ₁ maybe, for example, a directional coupler such as a star coupler. Thelight-to-electric converter 216 ₁ may be, for example, a solar cell or asemiconductor junction. The output of block 216 ₁ is electrical energy.The electrical energy is coupled from block 216 ₁ by way of a path 217 ₁to terminals or electrodes 210 e 1 and/or 212 e 1 of blocks 210 and 212,respectively, for energization of those portions requiring electricalpower. That portion of the light which is not coupled from optical fiber16 f of FIG. 2 at location 14 ₁ proceeds along fiber 16 f and eventuallyarrives at location 14 ₂. At location 14 ₂ of FIG. 2, a portion of thelight propagating through optical fiber 16 f is coupled by way of anoptical sampler or coupler, such as directional coupler 214 ₂, to alight-to-electric converter illustrated as a block 216 ₂. Thelight-to-electric converter 216 ₂ may be a solar cell or a semiconductorjunction. The output of block 216 ₂ is electrical energy. The electricalenergy is coupled from block 216 ₂ by way of path 217 ₂ to terminals orelectrodes 210 e 2 andor 212 e 2 of blocks 210 ₂ and 212 ₂,respectively, for energization of those portions requiring electricalpower.

[0019] Those skilled in the art know that the coupling of opticalsamplers can be selected or controlled so that no more energy isextracted from the propagating light power than is needed at a givenlocation, and that portion of the light which is not extracted fromoptical fiber 16 f at a given location propagates “downstream” towardother locations or, after the last location, toward remote end 16 re.

[0020] Those skilled in the art also know that a directional couplersuch as directional coupler 214 ₁ of FIG. 2 allows signal to be insertedonto a bus with low loss to the signal flowing on the main signal path16 c. In operation, the light propagates downstream from ship 2 of FIG.1 toward each location 14 ₁, 14 ₂, . . . and a portion of the light isextracted at each location for powering the sensor or sensor suite atthat location (if necessary) andor any ancillary equipment at thatlocation, such as the telemetry equipment at that location. The sensorsuites at the various locations operate, producing sensed signalsrelated to the location in question. The sensed signals at each locationare coupled to the telemetry equipment at that location, which processesthe signals, and multiplexes them (if necessary) for transmission overthe conductor 16 c. One effective means for multiplexing is the use of adifferent carrier frequency for each location, in which case thedemultiplexing block 22 of FIG. 1 would include frequency-selectivefilters. Another multiplexing technique is the use of code-divisionmultiplex, in which case demultiplexing block 22 would include codedivision equipment. Other multiplexing and demultiplexing schemes areknown and may be used. Multiplexing would not be necessary in the eventthat sufficient individual channels were available through the tensionelement 16, as might be the case if there were a separate conductor 16 cfor each location, rather than a single conductor 16 c as illustrated.

[0021] The light provided to a light-to-electric converter, such as 214₁ or 214 ₂ of FIG. 2, could be applied to a single light-to-electricconversion cell. Such cells usually have a maximum output voltage, whichmay be, for example 0.7 volts. This may not be sufficient voltage tooperate some electrically powered equipment. FIG. 3 is a simplifieddiagram in block and schematic form which illustrates details of oneembodiment of light-to-electric converter, illustrated as converter 216₂ for definiteness. In FIG. 3, light propagates from the tap of coupler214 ₂ by way of an optical path 310 to a further star coupler 312, whichdivides the light received from path 310 into a plurality of opticalfibers. A plurality 314 of cascaded optical converters 314 a, 314 b, . .. , 314 c is illustrated by diode symbols. These converters may be solarcells, optoelectric diodes, or the like, which produce voltage inresponse to application of light thereto. By being electrically coupledin series in a cascade, converters 314, when illuminated, are capable ofproducing a voltage equal to the sum of their individual voltages. Theoptical star coupler 312 provides light by way of a plurality of opticalfibers, designated together as 316, to the plural, cascaded orseries-connected light-to-electric converters 314 a, 314 b, . . . , 314c, thereby producing a voltage which becomes available on conductor 217₂ for use by utilization apparatus, which in the case of FIG. 2corresponds to at least the electricity users in telemetry block 212 ₂.

[0022]FIG. 4 is a simplified diagram in block and schematic formillustrating one possible arrangement which may be included in a sensorsuite, such as sensor suite 210 ₂ of FIG. 2. In FIG. 4, sensor suite 210₂ is illustrated as including a passive accelerometer 410, whichproduces signals for application to an electrically powered integratorblock 412. Electrical power is applied to block 412 by way of electricalinput port 210 e 2 and 412 e of FIG. 4. Processing 412 may include ananalog-to-digital converter coupled with a digital accumulator, as knownin the art.

[0023] In a preferred embodiment of the invention, each sensor suitecomprises an integrated MEMS (micro-electromechanical) sensor chipcontaining one or more acoustic or non-acoustic sensing elements andassociated signal conditioning electronics. Fabrication of such MEMSchips is accomplished using photolithography techniques, for example,similar to those used for fabrication of integrated circuits. A solarcell formed on each MEMS chip is operated for receiving input opticalpower from optical fiber 16 f and converting the optical power intoelectrical power for driving the electronics on the MEMS sensor chip.Long metal cable conductors for the provision of electrical power arethus eliminated from the towed array, thereby reducing the per-unitweight, and therefore the corresponding diameter of the cable arrayrequired to maintain neutral buoyancy of the array. The transmission ofthe sensed array information through the towing cable by way of anoptical fiber(s) rather than by way of an electrical cable conductor settends to further reduce the per-unit weight of the towing cable.

[0024]FIG. 5 is a simplified diagram in block and schematic form,illustrating a first preferred embodiment according to an aspect of theinvention. In FIG. 5, the wet end of the array 12 is designated 1, andthe dry end with processing is designated 2. The array 12 includes aline array 512 of four fiber optic acoustic sensors 512 ₁, 512 ₂, 512 ₃,512 ₄ connected by optical fiber 516 f ₁ to a photonics unit 520 locatedin dry portion 2 for receiving light therefrom, and also connected byway of an optical fiber 516 f ₂ to a telemetry unit 521, fortransmitting information thereto.

[0025] Also in FIG. 5, an array 540 of MEMS non-acoustic sensorsincludes non-acoustic MEMS sensors 540 ₁, 540 ₂, 540 ₃, and 540 ₄ forgenerating other sensed signals. At least some of the non-acoustic MEMSsensors are co-located with corresponding ones of the fiber acousticsensors of array 514. As illustrated, each non-acoustic MEMS sensor 540₁, 540 ₂, 540 ₃, and 540 ₄ is co-located with a fiber acoustic sensor512 ₁, 512 ₂, 512 ₃, and 512 ₄, respectively. Operating energy isprovided from photonics unit 520 to array 540 by way of a first portion516 f ₃ 1 of an optical fiber 516 f ₃, and each element 540 ₁, 540 ₂,540 ₃, and 540 ₄ of array 540 extracts a portion of the light energy forenergizing its operation. As described in conjunction with FIG. 3, thelight energy can be converted into electrical energy for energizationpurposes. The array 540 of MEMS sensors 540 ₁, 540 ₂, 540 ₃, and 540 ₄includes encodes the sensed information for transmission over a secondportion 516 f ₃ 2 of optical fiber 516 f ₃. Second portion 516 f ₃ 2 ofoptical fiber 516 f ₃ carries the sensed information in photonic form totelemetry unit 521 of FIG. 5.

[0026] In FIG. 5, telemetry unit 521 receives the sensed signalinformation, and separates it if necessary. An optical-to-digitalconverter 522 converts the optical signals into electrical digitalsignals suitable for processing by block 524. The processed signals aremade available to a display 526.

[0027]FIG. 6 is similar to FIG. 5, and corresponding elements aredesignated by like reference numerals. In FIG. 6, the MEMS sensor array640 includes MEMS sensors 640 ₁, 640 ₂, 640 ₃, and 640 ₄, at least someof which provide both acoustic and non-acoustic sensing functions.

[0028] Other embodiments of the invention will be apparent to thoseskilled in the art. For example, Another embodiment of the insertioncould be a mix of Fiber Optic, MEMS and conventional Non-MEMS sensors701, 702, 703 such as magnetic heading sensors and/or conventionalceramic sensors, as shown in FIG. 7.

[0029] Thus, an array (12) according to an aspect of the inventionincludes at least a first sensor (210 ₁) for sensing an environmentalcondition and for generating a first signal (211 ₁) in response thereto,and a second sensor (210 ₂) for sensing the environmental condition andfor generating a second signal (211 ₂) in response thereto. A tensionelement (16) is coupled to the first (210 ₁ ) and second (210 ₂) sensorsfor tending to keep the first (210 ₁) and second (210 ₂) sensors atfirst (14 ₁) and second (14 ₂) locations separated by a physical spacing(S) no greater than a given amount. A first electrically operatedtransducer (210 ₁) is co-located with the first sensor (210 ₁) andelectrically coupled thereto for receiving the first signal (211 ₁) andfor transmitting at least a signal (213 ₁) related to the first signal(211 ₁) to a node (2) of the array (12). A second electrically operatedtransducer (210 ₂) is co-located with the second sensor (210 ₂) andelectrically coupled thereto for receiving the second signal (211 ₂) andfor transmitting at least a signal (213 ₂) related to the second signal(211 ₂) to a node (2) of the array (12). The first (212 ₁) and second(212 ₂) electrically operated transducers each include a terminal (212 e1 and 212 e 2, respectively) for receiving energizing potential. Alight-carrying optical fiber (16 f) extends between the first and secondlocations. A light-to-electric converter (216 ₁, 216 ₂) located at eachof the first (14 ₁) and second (14 ₂) locations receives light from theoptical fiber (16 f), and converts the light into the energizingpotential.

[0030] In a particular version of this aspect of the invention, at leastsome of the sensors (210 ₁, 210 ₂) comprise pressure sensors, and maycomprise acoustic pressure sensors. In another version of this aspect,the tension element (16) may comprise the optical fiber. In one versionof this aspect of the invention, the light-to-electric converter (216 ₁,216 ₂) may comprise a solar cell, and in another version thelight-to-electric converter comprises a photodiode.

[0031] In another version of this aspect of the invention, the firstsensor (210 ₁) may comprise an acceleration sensor (410), and anintegrator (412) coupled to the acceleration sensor (410) for convertingacceleration signals into velocity signals. In a particular version ofthis aspect, the integrator (412) is an electrically operated integratorincluding a terminal (412 e) for receiving the energizing potential. Theacceleration sensor (410) may include a micro electro mechanical system(MEMS).

What is claimed is:
 1. An array of sensors, spaced apart by a tensionelement, said array comprising: a first sensor for sensing anenvironmental condition and for generating a first signal in responsethereto; a second sensor for sensing said environmental condition andfor generating a second signal in response thereto; a tension elementcoupled to said first and second sensors for tending to keep said firstand second sensors at first and second locations separated by a physicalspacing no greater than a given amount; a first electrically operatedtransducer co-located with said first sensor and coupled thereto forreceiving said first signal and for transmitting at least a signalrelated to said first signal to a node of said array, said firstelectrically operated transducer including a terminal for receivingenergizing potential; a second electrically operated transducerco-located with said second sensor and coupled thereto for receivingsaid second signal and for transmitting at least a signal related tosaid second signal to a node of said array, said second electricallyoperated transducer including a terminal for receiving energizingpotential; a light-carrying optical fiber extending between said firstand second locations; and a light-to-electric converter located at eachof said first and second locations for receiving light from said opticalfiber, and for converting said light into said energizing potential. 2.An array according to claim 1, wherein at least some of said sensorscomprise pressure sensors.
 3. An array according to claim 1, whereinsaid tension element comprises said optical fiber.
 4. An array accordingto claim 1, wherein said light-to-electric converter comprises a solarcell.
 5. An array according to claim 1, wherein said light-to-electricconverter comprises a photodiode.
 6. An array according to claim 1,wherein said first sensor comprises: an acceleration sensor; and anintegrator coupled to said acceleration sensor for convertingacceleration signals into velocity signals.
 7. An array according toclaim 6, wherein said integrator is an electrically operated integratorincluding a terminal for receiving said energizing potential.
 8. Anarray according to claim 6, wherein said acceleration sensor is a microelectro mechanical system.
 9. An array according to claim 1, whereinsaid light-to-electric converter comprises a light coupler coupled tosaid optical fiber for coupling a sample of said light from said opticalfiber.
 10. An array according to claim 9, wherein said light coupler isdirectional.
 11. An array according to claim 1, further comprising anarray of fiber acoustic sensors at locations along said tension element,said array of fiber acoustic sensors being coupled to a source of lightby a further optical fiber, and producing sensed signals on a thirdoptical fiber.
 12. An array according to claim 11, wherein at least someof said fiber acoustic sensors of said array of fiber acoustic sensorsare co-located with said first and second sensors.
 13. An arrayaccording to claim 1, wherein the first sensor comprises a micro electromechanical system (MEMs) circuit formed on an electronic chip.
 14. Anarray according to claim 13, wherein the light to electric convertercomprises a solar cell formed on said electronic chip.
 15. An arrayaccording to claim 14, wherein said at least one signal related to saidfirst signal from said first transducer comprises an encoded opticalsignal for propagation to said node of said array.